Optical connector and optical connection structure

ABSTRACT

An optical connector includes an optical fiber including a glass fiber and a resin coating surrounding the glass fiber; a ferrule having a flange outside the ferrule and holding, inside the ferrule, a portion of the glass fiber exposed from the resin coating at an end of the optical fiber; a plug frame accommodating the ferrule; and an elastic member abutting the flange and biasing the ferrule forward in an optical axis direction of the optical fiber to retain the ferrule inside the plug frame. The flange and the plug frame have a protrusion and a recess that allow the flange and the plug frame to be fitted to each other at the predetermined position. When the ferrule is moved rearward in the optical axis direction, the protrusion and the recess are released from each other to bring the ferrule into a floating state relative to the plug frame.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to optical connectors and opticalconnection structures, and specifically to an optical connector and anoptical connection structure that include a ferrule with a flange, anelastic member biasing the ferrule, and a plug frame accommodating theferrule and the elastic member.

Description of the Related Art

With the widespread use of information and communication technologiessuch as the Internet, the construction of optical networks isprogressing to support high-speed communication and increased volumes ofinformation as well as two-way communication and high-volumecommunication. Optical connectors are used to connect network devices toeach other in data centers and to connect optical fibers to premisesreceiving equipment in subscriber optical communication systems.

An optical connector includes a ferrule holding an optical fiber and aplug frame accommodating the ferrule. A flange is disposed outside theferrule. The flange is biased in the optical axis direction of theoptical fiber. The optical connector is coupled to another opticalconnector with a sleeve therebetween, and the cores of the opticalfibers are optically connected together to form an optical connectionstructure.

Optical connection structures need to maintain an optical connectionbetween cores when an external force is applied to a plug frame.Accordingly, Ryo Nagase et al., “MU-Type Multicore Fiber Connector”,Proceedings of the 61^(st) IWCS Conference (2012) (Non-PatentLiterature 1) discloses a structure for allowing a ferrule and a flangeto float relative to a plug frame (plug housing) so that an externalforce applied to the plug frame is not transmitted to the ferrule or theflange.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical connectorand an optical connection structure that require fewer components andthat have a simpler structure.

To achieve the object, there is provided an optical connector includingan optical fiber, a ferrule, a plug frame, and an elastic member andconfigured to connect the optical fiber to another optical fiber at anend of the optical connector. The optical fiber includes a glass fiberand a resin coating surrounding the glass fiber. The ferrule has aflange outside the ferrule and a through-hole inside the ferrule andholds, in the through-hole, a portion of the glass fiber exposed fromthe resin coating at an end of the optical fiber. The plug frameaccommodates the ferrule. The elastic member abuts the flange and biasesthe ferrule parallel to a central axis of the through-hole toward an endface side of the ferrule where an end face of the optical fiber isexposed. The flange and the plug frame of the optical connector have aprotrusion and a recess, respectively, or a recess and a protrusion,respectively, that are configured to fit to each other. The opticalconnector is configured such that, when the ferrule is moved away fromthe end of the optical connector, the protrusion and the recess arereleased from each other to bring the ferrule into a floating staterelative to the plug frame.

The flange of the optical connector of the present invention may havethe protrusion on an outer peripheral surface of the flange. The plugframe may have the recess in an inner peripheral surface of the plugframe such that the recess guides the protrusion parallel to the centralaxis of the through-hole and a clearance into which the protrusion doesnot fit on a side of the recess facing away from the end of the opticalconnector. In this case, the plug frame may have a tapered surface on aside of the clearance facing the recess such that an inner space istapered toward the recess. In addition, the recess may become graduallynarrower toward the end of the optical connector. The protrusion maybecome gradually narrower toward the end of the optical connector.Furthermore, the flange may have a tapered surface such that the flangeis tapered toward the end of the optical connector. The optical fibermay be a single-mode fiber, a multicore fiber, apolarization-maintaining fiber, or a fiber bundle. The ferrule ispreferably formed of zirconia.

According to another aspect of the present invention, there is providedan optical connection structure including the optical connector of thepresent invention and a connection target coupled to the opticalconnector of the present invention with a sleeve therebetween. The twooptical fibers are optically connected together. The protrusion and therecess are released from each other and the ferrule is in the floatingstate relative to the plug flame when the ferrule is inserted into thesleeve and is moved rearward in an optical axis direction relative to apredetermined position of the plug frame.

The optical connector and the optical connection structure of thepresent invention require fewer components and have a simpler structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of an optical connector accordingto an embodiment of the present invention.

FIG. 2 is a perspective view of a ferrule included in the opticalconnector in FIG. 1.

FIG. 3 is a partial sectional view showing the optical connector in FIG.1 before the accommodation of the ferrule into a plug frame.

FIG. 4 is a perspective view of a front housing of the optical connectorin FIG. 1.

FIG. 5A is a sectional view of the front housing as viewed in thedirection of the arrows A-A in FIG. 4, and FIG. 5B is a sectional viewof the front housing as viewed in the direction of the arrows B-B inFIG. 4.

FIG. 6 is a partial sectional view showing the optical connector in FIG.1 as it opposes another optical connector with a split sleevetherebetween.

FIG. 7 is a partial sectional view showing the optical connector in FIG.1 as it is connected to the other optical connector with the splitsleeve therebetween.

FIG. 8 is a conceptual diagram illustrating a fiber bundle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of optical connectors and optical connectionstructures according to the present invention will now be described withreference to the attached drawings.

The structure in Non-Patent Literature 1 has a coupling component(Oldham coupling mechanism) between the flange and the plug frame. Theferrule is movable relative to the coupling component in a firstdirection perpendicular to the central axis of the ferrule. The couplingcomponent is movable relative to the plug frame in a second directionperpendicular to both the central axis of the ferrule and the firstdirection. In this structure, the flange is divided into a plurality ofsegments movable in the first and second directions; therefore, theoptical connector requires an increased number of components and has acomplicated structure, which makes it difficult to reduce themanufacturing cost of the optical connector. In addition, Non-PatentLiterature 1 only discloses that the ferrule is allowed to float withinthe plug frame so that the ferrule is movable in a directionperpendicular to the central axis of the ferrule; it does not disclosethat the ferrule is allowed to float so that the ferrule is also movablein the direction of the central axis of the ferrule and is alsorotatable.

FIG. 1 is an external perspective view of an optical connector 1according to an embodiment of the present invention. The opticalconnector 1 includes a plug frame 20 accommodating a ferrule 10. A boot34 for protecting an optical fiber F is disposed at the rear end of theplug frame 20.

FIG. 2 is a perspective view of the ferrule 10 included in the opticalconnector 1. The ferrule 10 includes a ferrule body 11 extending in theX-axis direction shown in the figure. The ferrule body 11 is formed ofzirconia. The ferrule body 11 is cylindrical and holds therein a portionof a glass fiber exposed from a resin coating at the distal end of theoptical fiber F. The optical fiber F is, for example, a multicore fiberhaving multiple cores. The optical fiber F is attached to the ferrule 10by inserting the optical fiber F into the rear end 13 of the ferrulebody 11 and exposing the distal end face of the optical fiber F at thefront end 12 of the ferrule body 11 such that the multiple cores arelocated at predetermined positions around the central axis of theferrule 10. The X-axis direction shown in the figure corresponds to theoptical axis direction of the optical fiber F. A zirconia ferrulereflects less light at the end face thereof than a metal ferrule.

A flange 14 is disposed at a substantially central position outside theferrule body 11. The flange 14 has a substantially quadrangularcross-section and has a top surface 15, a bottom surface 16, and sidesurfaces 17 forming the outer peripheral surface of the flange 14. Thetop surface 15 and the bottom surface 16 are flat surfaces parallel toeach other at a predetermined distance in the Z-axis direction shown inthe figure. The side surfaces 17 are flat surfaces parallel to eachother at a predetermined distance in the Y-axis direction shown in thefigure. The flange 14 also has tapered surfaces 15 a in the top surface15 thereof and tapered surfaces 17 a in the side surfaces 17 thereofsuch that the flange 14 is tapered in the positive direction of theX-axis shown in the figure. The flange 14 becomes gradually thinneralong the tapered surfaces 15 a and becomes gradually narrower along thetapered surfaces 17 a. Although not visible in FIG. 2, the flange 14also has similar tapered surfaces in the bottom surface 16 thereof. Thetapered surfaces 15 a and 17 a facilitate insertion of the ferrule 10from the rear side of the plug frame 20. As the ferrule 10 advancesfurther, the gap between the flange 14 and the plug frame 20 becomessmaller, which facilitates alignment of the ferrule 10 to the plug frame20.

The flange 14 has a key 18 on the top surface 15 thereof, for example,near the front end thereof. The key 18 protrudes outward in the radialdirection of the ferrule 10 (e.g., in the positive direction of theZ-axis shown in the figure). The key 18 has a substantially quadrangularcross-section, as does the flange 14, and has key side surfaces 18 cparallel to each other at a predetermined distance in the Y-axisdirection shown in the figure. The key 18 corresponds to the protrusionof the present invention. The key 18 also has tapered surfaces 18 a and18 b near the front end thereof such that the key 18 is tapered in thepositive direction of the X-axis shown in the figure. The key 18 becomesgradually narrower along the tapered surfaces 18 a and becomes graduallythinner along the tapered surface 18 b. The ferrule 10 with the flange14 is accommodated in the plug frame 20.

FIG. 3 is a sectional view showing the optical connector 1 before theaccommodation of the ferrule 10 into the plug frame 20. The plug frame20 has a quadrangular tubular front housing 21 on the front side thereof(on the side where the ferrule 10 is exposed from the plug frame 20 inthe X-axis direction shown in the figure) and a rear housing 31 on therear side thereof. The front housing 21 accommodates the distal portionof the ferrule 10. The rear housing 31 accommodates the rear portion ofthe ferrule 10 and a coil spring 19.

FIG. 4 is a perspective view of the front housing 21. The front housing21 is formed of resin. The front housing 21 has a rear end opening 24having a square shape and capable of receiving the ferrule 10 with theflange 14 and a front end opening 23 from which the front end 12 of theferrule body 11 protrudes. A flexible latch arm 22 is disposed on theouter peripheral surface of the front housing 21.

FIG. 5A is a sectional view of the front housing 21 as viewed in thedirection of the arrows A-A in FIG. 4, and FIG. 5B is a sectional viewof the front housing 21 as viewed in the direction of the arrows B-B inFIG. 4. The front housing 21 has a top surface 25, a bottom surface 26,and side surfaces 27 inside the front housing 21. The top surface 25 andthe bottom surface 26 are parallel to each other at a predetermineddistance in the Z-axis direction shown in the figures. The side surfaces27 are parallel to each other at a predetermined distance in the Y-axisdirection shown in the figures. There is a keyway 28 in the top surface25. The keyway 28 corresponds to the recess of the present invention.

Specifically, the keyway 28 is recessed in the positive direction of theZ-axis shown in the figure. The keyway 28 has guide surfaces 28 a thatface the key side surfaces 18 c (FIG. 2) and is configured to guide thekey 18 in the X-axis direction shown in the figure. The width betweenthe guide surfaces 28 a becomes gradually smaller in the positivedirection of the X-axis, and the keyway 28 also becomes graduallyshallower in the positive direction of the X-axis. Since the key 18becomes gradually thinner in the positive direction of the X-axis, thekey 18 fits more tightly into the keyway 28 as the flange 14 advances,which allows the ferrule 10 to be reliably aligned to the front housing21.

The front housing 21 also has tapered surfaces 30 a in the top surface25 thereof, a tapered surface 30 in the bottom surface 26 thereof, andtapered surfaces 30 b in the side surfaces 27 thereof such that theinner space is tapered in the positive direction of the X-axis shown inthe figure. The tapered surface 30 is first described by way of example.The distance between the top surface 25 and the bottom surface 26 on theopening 23 side (the front side) of the keyway 28 is shorter than thedistance between the top surface 25 and the bottom surface 26 on theopening 24 side (the rear side) of the keyway 28, and they are joinedtogether by the tapered surface 30, which rises gradually in thepositive direction of the X-axis shown in the figure. The taperedsurfaces 30 b are described next by way of example. The width betweenthe side surfaces 27 on the front side of the keyway 28 is shorter thanthe width between the side surfaces 27 on the rear side of the keyway28.

In this way, the height and width of the inner space of the fronthousing 21 of the plug frame 20 become gradually shorter in the forwarddirection, which facilitates insertion of the ferrule 10 from the rearside of the front housing 21. As the ferrule 10 advances further, thegap between the outer peripheral surface of the flange 14 and the innerperipheral surface of the front housing 21 becomes smaller, whichfacilitates alignment of the ferrule 10 to the front housing 21.

On the other hand, there is no keyway 28 in the portion of the topsurface 25 shown in FIG. 5B. As shown in FIG. 3, there is a clearance 29into which the key 18 does not fit on the rear side of the keyway 28 (inthe negative direction of the X-axis shown in the figure; the sameapplies hereinafter). Specifically, the clearance 29 is a quadrangulartubular inner space defined by the top surface 25, the bottom surface26, and the side surfaces 27. The distance between the top surface 25and the bottom surface 26 (the length in the Z-axis direction shown inthe figure; the same applies hereinafter) is longer than the thicknessof the flange 14 including the key 18. The ferrule 10 with the flange 14is allowed to float when the flange 14 is located at the clearance 29.By providing the keyway 28 and the clearance 29, an aligned state and afloating state can be easily achieved.

The rear housing 31 is formed of, for example, resin. As shown in FIG.3, the rear housing 31 has a cylindrical spring-accommodating part 33capable of accommodating the rear portion of the ferrule 10 and the coilspring 19. The coil spring 19 is disposed on the rear side of theferrule 10 and is brought into abutment with the rear end of the flange14 to bias the ferrule 10 forward (in the positive direction of theX-axis shown in the figure; the same applies hereinafter). The coilspring 19 corresponds to the elastic member of the present invention.

A clip 32 capable of engaging with the latch arm 22 is disposed on theouter peripheral surface of the rear housing 31. The rear portion of theferrule 10 and the coil spring 19 are accommodated into the rear housing31, whereas the distal portion of the ferrule 10 is inserted into thefront housing 21. At this time, the flange 14 is placed on the bottomsurface 26 of the front housing 21 when located at the clearance 29.

FIG. 6 is a sectional view showing the optical connector 1 in FIG. 1 asit opposes another optical connector 1′ with a split sleeve 40therebetween. As the clip 32 moves onto the latch arm 22, the fronthousing 21 is latched to the rear housing 31. At the same time, theflange 14 is pushed forward by the biasing force of the coil spring 19and is quickly moved forward along the tapered surfaces 30, 30 a, and 30b of the front housing 21. When the flange 14 reaches the taperedsurfaces 30, 30 a, and 30 b, the key 18 of the flange 14 starts fittinginto the keyway 28 of the front housing 21.

The tapered surfaces 18 a and 18 b of the key 18 enter the keyway 28. Asthe ferrule 10 advances further, the key side surfaces 18 c of the key18 come into tight contact with the guide surfaces 28 a of the keyway28. When the flange 14 and the front housing 21 are fitted to eachother, the ferrule 10 is aligned at a position where the ferrule 10 hasits distal portion protruding from the front housing 21. In this state,the ferrule 10 is difficult to move in any of the X-axis, Y-axis, andZ-axis directions and is also difficult to rotate about the opticalaxis.

FIG. 7 is a partial sectional view of an embodiment of an opticalconnection structure of the present invention in which the opticalconnector 1 is connected to the other optical connector 1′ with thesplit sleeve 40 therebetween. The optical connection structure includesthe optical connector 1 and the other optical connector P. The splitsleeve 40 (the sleeve of the present invention) is used to opticallyconnect the optical fiber F on the optical connector 1 side to anoptical fiber F′ (not shown) on the optical connector 1′ side. Theoptical fiber F′ is a multicore fiber having multiple cores. The opticalfiber F′ is attached to a ferrule 10′ such that the multiple cores arelocated at predetermined positions around the central axis of theferrule 10′.

Although not shown in cross-section, the optical connector 1′ isconfigured in the same manner as the optical connector 1 and includes aplug frame 20′ accommodating the ferrule 10′ holding the optical fiberF′ and an elastic member (not shown) biasing the ferrule 10′. Theoptical connector 1′, which corresponds to the connection target of thepresent invention, may be replaced by an optical plug.

The split sleeve 40 has an inner diameter substantially equal to, orslightly smaller than, the diameter of the ferrules 10 and 10′. Thesplit sleeve 40 has a slit (not shown) that can be widened to increasethe inner diameter thereof. The split sleeve 40 may be incorporated intoan adaptor (not shown).

The ferrule 10 is inserted into one end of the split sleeve 40, whereasthe ferrule 10′ is inserted into the other end of the split sleeve 40.The end face of the optical fiber F on the ferrule 10 side and the endface of the optical fiber F′ on the ferrule 10′ side are brought intosurface contact with each other in the split sleeve 40. As the splitsleeve 40 enters the front housing 21 and the ferrule 10 is movedrearward, the flange 14 is moved rearward against the biasing force ofthe coil spring 19, with the result that the key 18 is released from thekeyway 28. When the flange 14 is moved to the clearance 29, the ferrule10 is brought into a floating state relative to the front housing 21. Inthis state, the ferrule 10 is movable in any of the X-axis, Y-axis, andZ-axis directions and is also rotatable about the optical axis togetherwith the optical fiber F′ on the optical connector 1′ side.

In this way, the key 18 of the flange 14 is fitted in the keyway 28 ofthe front housing 21 until the optical connector 1 is coupled to theoptical connector 1′ (until the ferrule 10 is moved from the front sideto the rear side), which allows the ferrule 10 to be aligned to thefront housing 21 and also prevents rotation. Thus, when the plug frame20 is opposed to the plug frame 20′, the multiple cores included in theoptical fiber F can be accurately opposed to the multiple cores includedin the optical fiber F′.

On the other hand, after the optical connector 1 is coupled to theoptical connector 1′ (after the ferrule 10 is moved to the rear side,i.e., when the connectors 1 and 1′ are connected together), the key 18is released from the keyway 28 to allow the ferrule 10 to float relativeto the front housing 21. When an external force is applied to the fronthousing 21 or the rear housing 31, the external force is not transmittedto the ferrule 10, so that the optical connection between the twooptical fibers F and F′ can be maintained.

In this way, an aligned state and a floating state are achieved simplyby providing the key 18 and the keyway 28. Thus, the optical connector 1requires fewer components and has a simpler structure. As a result, anoptical connection structure in which an optical connection can beeasily maintained with a simple structure can be provided.

Although an example in which the flange 14 has the key 18 and the fronthousing 21 has the keyway 28 has been described in the foregoingembodiment, the present invention is not limited to this example;instead, the flange may have the keyway, and the front housing may havethe key. Although LC connectors have been described as examples ofoptical connectors in the foregoing embodiment, the present inventioncan also be applied to other types of optical connectors, including, forexample, SC connectors and MU connectors.

Furthermore, although a multicore fiber has been described as an exampleof the optical fiber F, the optical fiber of the present invention mayalso be, for example, a single-mode fiber, a polarization-maintainingfiber, or a fiber bundle. Multicore fibers, polarization-maintainingfibers, and fiber bundles are optical fibers that require the adjustmentof the angle of rotation about the central axis when opticallyconnected.

Although not shown, a polarization-maintaining fiber (e.g., astress-induced polarization-maintaining fiber) has circularstress-inducing parts disposed on both sides of a core. Whereas asingle-mode fiber has two modes with orthogonal planes of polarization(polarization modes), a polarization-maintaining fiber creates adifference in propagation constant between these two polarization modesto reduce the coupling of one polarization mode to the otherpolarization mode, thereby achieving an enhancedpolarization-maintaining ability.

A fiber bundle is a bundle of single-core fibers for optical connectionto a multicore fiber. Specifically, for example, ends of single-corefibers with a glass diameter of 125 μm are chemically etched to a glassdiameter of 45 μm. As shown in FIG. 8, a plurality of (e.g., seven)fibers are inserted together into the ferrule 10 with an adhesive. Inthis example, the fibers can be arranged such that the core-to-coredistance is 45 μm. In this way, it is possible to reliably align notonly single-mode fibers, but also multicore fibers,polarization-maintaining fibers, and fiber bundles, thereby achieving areduction in connection loss.

The embodiments disclosed herein are to be considered in all respects asillustrative and not restrictive. The scope of the invention isindicated by the claims, rather than by the foregoing meaning, and allchanges that come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. An optical connector comprising: an optical fibercomprising a glass fiber and a resin coating surrounding the glassfiber; a ferrule having a front end and a rear end, the ferrule having aflange outside the ferrule and between the front end and rear end of theferrule, and the ferrule having a through-hole inside the ferrule, theferrule holding, in the through-hole, a portion of the glass fiberexposed from the resin coating at an end of the optical fiber; a plugframe accommodating the ferrule; and an elastic member abutting theflange and biasing the ferrule parallel to a central axis of thethrough-hole toward an end face side of the ferrule where an end face ofthe optical fiber is exposed, the optical connector being configured toconnect the optical fiber to another optical fiber at an end of theoptical connector, wherein the flange and the plug frame have aprotrusion and a recess, respectively, or a recess and a protrusion,respectively, that are configured to fit to each other, wherein, whenthe ferrule is moved away from the end of the optical connector, theprotrusion and the recess are released from each other to bring theferrule into a floating state relative to the plug frame, and wherein,in the floating state, the ferrule is accommodated in the plug frame andthe front end and the rear end of the ferrule and the flange of theferrule are movable relative to one another in both axial and rotationaldirections.
 2. The optical connector according to claim 1, wherein theflange has the protrusion on an outer peripheral surface of the flange,and the plug frame has the recess in an inner peripheral surface of theplug frame such that the recess guides the protrusion parallel to thecentral axis of the through-hole and a clearance into which theprotrusion does not fit on a side of the recess facing away from the endof the optical connector.
 3. The optical connector according to claim 2,wherein the plug frame has a tapered surface on a side of the clearancefacing the recess such that an inner space is tapered toward the recess.4. The optical connector according to claim 1, wherein the recessbecomes gradually narrower toward the end of the optical connector. 5.The optical connector according to claim 1, wherein the flange has atapered surface such that the flange is tapered toward the end of theoptical connector.
 6. The optical connector according to claim 1,wherein the protrusion becomes gradually narrower toward the end of theoptical connector.
 7. The optical connector according to claim 1,wherein the optical fiber is a single-mode fiber, a multicore fiber, apolarization-maintaining fiber, or a fiber bundle.
 8. The opticalconnector according to claim 1, wherein the ferrule comprises zirconia.9. An optical connection structure comprising: the optical connectoraccording to claim 1; and a connection target coupled to the opticalconnector with a sleeve therebetween, wherein the two optical fibers areoptically connected together, and wherein the protrusion and the recessare released from each other and the ferrule is in the floating staterelative to the plug flame.
 10. The optical connector according to claim1, wherein, in the floating state, an end face of the optical fiber onthe end face side of the ferrule contacts an end face of another opticalfiber.